AME 83:167-179 (2019)  -  DOI: https://doi.org/10.3354/ame01909

ABSTRACT: The conversion of tropical forests into oil palm Elaeis guineensis (OP) monoculture alters stream physicochemical conditions, potentially threatening freshwater ecosystems. Understanding the responses of bacterial assemblages to environmental changes and riparian management efforts are vital for our understanding of stream ecosystem functioning. We used 16S rRNA gene sequencing techniques to investigate bacterial community dynamics on decomposing litter of 2 contrasting qualities, Macaranga tanarius and OP, in streams across a gradient of riparian disturbance in OP plantations. Bacterial community composition was more heavily influenced by litter quality, such as increased structural compounds (i.e. toughness, lignin, fibre) and nutrients in OP litter and increased secondary compounds in Macaranga litter, rather than changes in stream conditions due to different riparian buffer qualities. Bacterial colonization on Macaranga was susceptible to the increased stream temperatures and nutrients in OP streams, whereas significant alterations in bacterial community composition on OP litter were observed that were possibly due to long-term agricultural disturbances. Both litter species were dominated by Proteobacteria and Bacteroidetes with Chitinophaga and Caulobacteraceae contributing most to the differences observed. Compared to pristine streams, bacterial diversity and richness were significantly higher in OP streams with no buffer, whereas OP streams with forested riparian buffer and untreated buffer (i.e. no chemical inputs) had intermediate values. In conclusion, bacterial assemblages were regulated by the quality of litter. We therefore propose the retention of riparian vegetation with high tree diversity to mitigate impacts on the formation of litter bacterial assemblages and the ecosystem processes they mediate in oil palm plantation streams.

KEY WORDS: Bacterial decomposers · 16S rRNA genes · Oil palm plantations · Litter quality · Riparian buffer